The present invention relates generally to panel fasteners, and more particularly, panel fasteners adapted to receive a deflectable retaining ring.
Panel fasteners are inserted through a hole in the panel, and then a retaining ring is attached to the fastener""s threaded end. The retaining ring prevents the fastener from being extracted, yet still permits a nut to be threaded onto the fastener for securing the panel. The fastener is far less likely to be lost during disassembly and reassembly procedures.
A number of different approaches have been developed for attaching a retaining ring to a fastener. One approach involves forming a plurality of grooves or splines along the length of the fastener to receive inwardly-projecting tabs of the retaining ring. The splines extend fully to the end of the fastener opposite the head. After the retaining ring has been slid onto the fastener, an end cap is attached to the threaded end of the fastener, to close off the channels and prevent the ring from being removed. One disadvantage of this approach is that it cannot be easily or economically applied to hollow, internally-threaded fasteners.
In another approach, splines are formed along the length of the fastener, and a second set of splines is also formed along the fastener, interleaved with the first set. Both ends of each spline in the second set are so closed that a retaining ring cannot be longitudinally removed from the fastener when the retaining ring""s inwardly-directed tabs engage the second set of splines. Cross-over slots individually connect the first set of open-end splines with the second set of closed splines. The retaining ring is secured to the fastener by sliding its tabs along the open-end slots to the location of the cross-over slots, and then rotating the retaining ring so as to move the tabs over to the closed splines. Extraction of the fastener from the workpiece is prevented as long as the retaining ring tabs do not exit back through the cross-over slot and open-end splines.
Although this approach is suitable for internally-threaded fasteners, it is nevertheless subject to certain drawbacks. Fastener movement during disassembly procedures sometimes leads to rotation of the retaining ring with respect to the fastener. This rotation can occasionally re-position the retaining ring tabs in the open-end splines, thus permitting inadvertent release of the retaining ring from the fastener. In order to overcome this disadvantage, the cross-over slots are sometimes displaced longitudinally relative to each other so that the ring tabs can be moved from the closed splines to the open-end splines only when the ring is tilted at an extreme angle relative to the fastener shaft. While the likelihood of an inadvertent fastener release is reduced using this latter approach, inadvertent release through random movement of the fastener can still occur.
Consequently, a fastener retaining ring combination was developed that does not rely on the orientation of the fastener with respect to a retaining ring to keep the ring attached to the fastener, but still was suitable for fasteners of both internal and external thread configurations. The fastener/retaining ring assembly of U.S. Pat. No. 4,911,726 was developed, which discloses a fastener having a generally cylindrical shaft with a first spline extending longitudinally along the length of the shaft and terminating at one end of the shaft, with a second spline extending along the shaft, circumferentially spaced from the first spline and being closed at its opposite ends, and further with a slot interconnecting the first and second splines, the cross-over slot having a depth less than the depth of the second, closed-end spline. The fastener shaft is sized to slidably receive a retaining ring having an inwardly-projecting tab that is engageable with the first and second splines and the cross-over slot. The shallow depth of the cross-over slot required the retaining ring to significantly expand or flex outwardly to allow the inwardly-projecting tab to move from the first, open-end spline to the second, closed spline. The retaining ring thus resisted displacement of the tabs between the two splines, regardless of the relative orientation of the ring and shaft. The use of a closed-end spline on the shaft""s exterior surface obviated the need for an end cap, thereby making the fastener suitable for use with hollow, internally-threaded fasteners.
The fastener/ring assembly of U.S. Pat. No. 4,911,726 also disclosed an embodiment wherein the cross-over slot depth varied, thus forming a ramp leading from the first, open-end spline to the second, closed-end spline. The ramp facilitated insertion of the retaining ring tab into the closed-end spline, but did not affect the resistance to displacement of the tabs from the closed-end spline back into the open-end spline. The ramp could be smooth with a continuously varying depth, or was formed by two straight segments, or formed by a straight line segment and a continuous curve segment of constant depth.
To facilitate assembly, the retaining ring was placed in a standard hexagon socket wrench that encompasses the hexagonal exterior configuration of the retaining ring. At that point, the retaining ring was rotated clockwise over the cross-over ramp, and as the hexagon tool was rotated, the tabs engaged the ramp angle wherein the tabs reach maximum deflection on the cross-over ramp, and continued rotation caused the tabs to spring back into the closed-end slot.
The difficulty with this design is that the deflection is caused by the compressive buckling of the tabs and a portion of the outer hexagonal configuration of the retaining ring. The hexagon socket wrench engages near the corner of three of the six positions of the hexagon retaining ring. As the tabs climb up the ramp of the cross-over slot, a compressive load is transmitted through the tab to the driving surface of the hexagon socket wrench. It becomes readily apparent that the deflection occurs only in the portion of the tab of the retaining ring between the socket and the surfaces of the cross-over ramp. At this point, a compressive buckling occurs, and the actual amount of deflection is minimal. Due to the short length between the end of the tab engagement area and the hexagon socket surface, the compressive buckling load is excessive and results in material deformation of the tab end surface and the cross-over ramp surfaces. Depending on tolerancing conditions and the degree of deformation and/or wear of the tabs after installation, performance of the hold-out nibs located in the closed-end splines of the fastener may be affected. In addition, the closed-end splines at the opposite end of the head of the fastener have an abrupt surface which prevents the retaining ring from being removed. Depending on the conditions and the degree of deformation and/or wear of the tabs after installation, can affect the retention capabilities of the panel fastener. Consequently, a need exists for a fastener/deflectable retaining ring assembly that eliminates the deficiencies of previous fastener/retaining ring assembly designs.
The present invention is a fastener and deflectable retaining ring assembly having a fastener with a generally cylindrical shaft with a plurality of first splines extending longitudinally along the length of the shaft and terminating at one end of the shaft, with a plurality of second splines extending along the shaft, circumferentially spaced from the first splines and being closed at its opposite ends, and further with a cross-over slot interconnected with the first and second splines, the cross-over slot having a depth less than the depth of the second closed-end splines. The fastener shaft is sized to slidably receive a generally triangular retaining ring having inwardly-projecting tabs that are engageable with the first and second splines and the cross-over slot. The shallow depth of the cross-over slot requires the retaining ring to flex to allow the inwardly-projecting tabs to move from the first, open-end splines to the second, closed splines. The retaining ring thus resists displacement of the tabs between the two splines, regardless of the relative orientation of the ring and the shaft.
The retaining ring design addresses all of the deficiencies of previous designs and resembles a slightly bulging triangle rather than a traditional hexagon of previous retaining rings. The tabs of the retaining ring are located midway between the corner segments of the triangle rather than at the corners of the hexagon on previous designs. The retaining ring of the present invention can utilize a hexagon socket wrench to install the ring on the panel fastener. The installation process includes aligning the tabs with the open-end splines and pushing the ring toward the head of the fastener until it stops against a back wall of the open-ended splines. The socket wrench is rotated clockwise until the tabs intersect the cross-over ramp, wherein further rotation causes the tabs to spring radially outward until reaching a flat surface in the cross-over slot. Continued rotation into the closed end splines results in the tabs to snap back to their original dimension. Since the tabs are located midway between the driving corners of the hexagon tool, there is no resistance of the tabs to deflect radially except where desired. With the triangular design, the hexagon tool does not constrain or limit the allowable deflection of the tabs to pass over the ramps in the cross-over slot. This design provides a considerable larger moment arm for allowable deflection as compared to previous designs. There is no compressive buckling, but rather a predictable beam deflection. As a result, there is no appreciable damage to the ends of the tabs or the ramps in the cross-over slot of the fastener. Furthermore, the tabs return to their original internal diameter, and there is improved holdout performance with the nibs located in the closed-end splines, which improves panel fastener retention. With this design, the deflection of the tabs becomes predictable and does not exceed the yield strength.
The novel features of the present invention will be better understood from the following detailed description, as considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are only for purposes of illustration and description and are not intended as a limiting definition of the present invention.